1. Field of the Invention
The present invention relates to an image display apparatus which displays an image by the emitted electrons, and control method of the apparatuses.
2. Description of the Related Art
Conventionally, two types of devices, namely hot and cold cathode devices, are known as electron-emitting devices. Known examples of the cold cathode devices are surface-conduction type emission devices, field emission type electron-emitting devices (to be referred to as FE type electron-emitting devices hereinafter), and metal/insulator/metal type electron-emitting devices (to be referred to as MIM type electron-emitting devices hereinafter).
Known examples of the FE type electron-emitting devices are described in W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d, Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical properties of thin-film field emission cathodes with molybdenium conesxe2x80x9d, J. Appl. Phys., 47, 5248 (1976).
A known example of the surface-conduction type emission devices is described in, e.g., M. I. Elinson, xe2x80x9cRadio Eng. Electron Phys., 10, 1290 (1965) and other examples will be described later.
The surface-conduction type emission device utilizes the phenomenon that electrons are emitted by a small-area thin film formed on a substrate by flowing a current parallel through the film surface. The surface-conduction type emission device includes electron-emitting devices using an Au thin film [G. Dittmer, xe2x80x9cThin Solid Filmsxe2x80x9d, 9,317 (1972)], an In2O3/SnO2 thin film [M. Hartwell and C. G. Fonstad, xe2x80x9cIEEE Trans. ED Conf.xe2x80x9d, 519 (1975)], a carbon thin film [Hisashi Araki et al., xe2x80x9cVacuumxe2x80x9d, Vol. 26, No. 1, p. 22 (1983)], and the like, in addition to an SnO2 thin film according to Elinson mentioned above.
FIG. 27 is a plan view showing the device by M. Hartwell et al. described above as a typical example of the device structures of these surface-conduction type emission devices. Referring to FIG. 27, reference numeral 3001 denotes a substrate; and 3004, a conductive thin film made of a metal oxide formed by sputtering. This conductive thin film 3004 has an H-shaped pattern, as shown in FIG. 27. An electron-emitting portion 3005 is formed by performing electrification processing (referred to as forming processing to be described later) with respect to the conductive thin film 3004. An interval L in FIG. 27 is set to 0.5 to 1 mm, and a width W is set to 0.1 mm.
In the conventional electron-emitting devices, the electron-emitting portion 3005 is generally formed by performing electrification processing called forming processing for the conductive thin film 3004. In the forming processing, for example, a DC voltage or a voltage which increases at a very low rate of, e.g., 1 V/min is applied across the conductive thin film 3004 to partially destroy or deform the conductive thin film 3004, thereby forming the electron-emitting portion 3005 with an electrically high resistance. Note that the electron-emitting portion 3005 is a fissure formed in part of the conductive thin film 3004. Electrons are emitted near the fissure by applying a predetermined voltage across the electron-emitting portion 3005.
FIG. 28 is a sectional view showing the device by C. A. Spindt et al. described above as a typical example of the FE type device structure. In FIG. 28, reference numeral 3010 denotes a substrate; 3011, emitter wiring made of a conductive material; 3012, an emitter cone; 3013, an insulating layer; and 3014, a gate electrode. In this device, a voltage is applied between the emitter cone 3012 and gate electrode 3014 to emit electrons from the distal end portion of the emitter cone 3012.
As another FE type device structure, there is an example in which an emitter and gate electrode are arranged on a substrate to be almost parallel to the surface of the substrate, in addition to the multilayered structure of FIG. 28.
A known example of the MIM type electron-emitting devices is described in C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devicesxe2x80x9d, J. Appl. Phys., 32,646 (1961). FIG. 29 shows a typical example of the MIM type device structure. FIG. 29 is a sectional view of the MIM type electron-emitting device. In FIG. 29, reference numeral 3020 denotes a substrate; 3021, a lower electrode made of a metal; 3022, a thin insulating layer having a thickness of about 100 xc3x85; and 3023, an upper electrode made of a metal and having a thickness of about 80 to 300 xc3x85. In the MIM type electron-emitting device, an appropriate voltage is applied between the upper and lower electrodes 3023 and 3021 to emit electrons from the surface of the upper electrode 3023.
Since the above-described cold cathode devices can emit electrons at a temperature lower than that for hot cathode devices, they do not require any heater. The cold cathode device has a structure simpler than that of the hot cathode device and can shrink in feature size. Even if a large number of devices are arranged on a substrate at a high density, problems such as heat fusion of the substrate hardly arise. In addition, the response speed of the cold cathode device is high, while the response speed of the hot cathode device is low because it operates upon heating by a heater. For this reason, applications of the cold cathode devices have enthusiastically been studied.
Of cold cathode devices, the above surface-conduction type emission devices have a simple structure and can be easily manufactured, and thus many devices can be formed on a wide area. As disclosed in Japanese Patent Laid-Open No. 64-31332 filed by the present applicant, a method of arranging and driving a lot of devices has been studied.
Regarding applications of the surface-conduction type emission devices to, e.g., image forming apparatuses such as an image display apparatus and an image recording apparatus, charge beam sources, and the like have been studied.
Particularly as an application to image display apparatuses, as disclosed in the U.S. Pat. No. 5,066,833 and Japanese Patent Laid-Open Nos. 2-257551 and 4-28137 filed by the present applicant, an image display apparatus using the combination of a surface-conduction type emission device and a fluorescent substance emits light upon reception of an electron beam has been studied. This type of image display apparatus using the combination of the surface-conduction type emission device and the fluorescent substance is expected to exhibit better characteristics than other conventional image display apparatuses. For example, compared with recent popular liquid crystal display apparatuses, the above display apparatus is superior in that it does not require any backlight because it is a self-emission type and that it has a wide view angle.
A method of driving a plurality of FE type electron-emitting devices arranged side by side is disclosed in, e.g., U.S. Pat. No. 4,904,895 filed by the present applicant. As a known example of an application of FE type electron-emitting devices to an image display apparatus is a flat display apparatus reported by R. Meyer et al. [R. Meyer: xe2x80x9cRecent Development on Microtips Display at LETIxe2x80x9d, Tech. Digest of 4th Int. Vacuum Microelectronics Conf., Nagahama, pp. 6-9 (1991)].
An example of an application of a larger number of MIM type electron-emitting devices arranged side by side to an image display apparatus is disclosed in Japanese Patent Laid-Open No. 3-55738 filed by the present applicant.
The present inventors have examined cold cathode devices of various materials, various manufacturing methods, and various structures, in addition to the above-mentioned conventional cold cathode devices. Further, the present inventors have made extensive studies on a multi electron source having a large number of cold cathode devices, and an image display apparatus using this multi electron source. The present inventors have examined a multi electron source having an electrical wiring method shown in, e.g., FIG. 30. That is, a large number of cold cathode devices are two-dimensionally arranged in a matrix to obtain a multi electron source, as shown in FIG. 30.
Referring to FIG. 30, reference numeral 4001 denotes a cold cathode device; 4002, a row wiring; and 4003, a column wiring. The row and column wirings 4002 and 4003 actually have finite electrical resistances, which are represented as wiring resistances 4004 and 4005 in FIG. 30. This wiring method is called a simple matrix wiring method. For the illustrative convenience, the multi electron source is illustrated in a 6xc3x976 matrix, but the size of the matrix is not limited to this. For example, in a multi electron source for an image display apparatus, a number of devices enough to perform desired image display are arranged and wired.
In a multi electron source constituted by arranging cold cathode devices in a simple matrix, appropriate electrical signals are applied to the row and column wirings 4002 and 4003 to output a desired electron beam. For example, to drive the cold cathode devices on an arbitrary row in the matrix, a selection voltage Vs is applied to the column wiring 4002 on the row to be selected, and at the same time a non-selection voltage Vns is applied to the row wirings 4002 on an unselected row. In synchronism with this, a driving voltage Ve for outputting an electron beam is applied to the column wiring 4003. According to this method, when voltage drops across the wiring resistances 4004 and 4005 are neglected, a voltage (Vexe2x88x92Vs) is applied to the cold cathode devices on the selected row, while a voltage (Vexe2x88x92Vns) is applied to the cold cathode devices on the unselected row. When the voltages Ve, Vs, and Vns are set to appropriate magnitudes, an electron beam having a desired intensity must be output from only the cold cathode device on the selected row. When different driving voltages Ve are applied to respective column wirings, electron beams having different intensities must be output from the respective devices of the selected row. A change in length of time for which the driving voltage Ve is applied necessarily causes a change in length of time for which an electron beam is output.
The multi electron source constituted by arranging cold cathode devices in a simple matrix has a variety of applications. For example, when an electrical signal corresponding to image information is appropriately applied, the multi electron source can be suitably used as an electron source for an image display apparatus.
FIG. 31 is a perspective view of an example of a display panel for a flat image display apparatus using the multi electron source where part of the panel is removed for showing the internal structure of the panel.
In FIG. 31, reference numeral 3115 denotes a rear plate; 3116, a side wall; and 3117, a face plate. The rear plate 3115, side wall 3116, and face plate 3117 form an envelope (airtight container) for keeping the interior of the display panel vacuum.
The rear plate 3115 is fixed to a substrate 3111. Nxc3x97M cold cathode devices 3112 are formed on the substrate 3111. Note that N and M are positive integers equal to 2 or more, and properly set in accordance with a target number of display pixels. The Nxc3x97M cold cathode devices 3112 are wired by M row wirings 3113 and N column wirings 3114, as shown in FIG. 31. The portion constituted by the substrate 3111, cold cathode devices 3112, and row and column wirings 3113 and 3114 will be referred to as a multi electron source. At an intersection of the row and column wirings 3113 and 3114, an insulating layer (not shown) is formed between them to maintain electrical insulation.
A fluorescent film 3118 is formed from a fluorescent substance under the face plate 3117, and colored in three, red (R), green (G), and blue (B) primary colors (see FIGS. 18A and 18B). A black conductive material (1010 in FIGS. 18A and 18B) is provided between fluorescent substances of respective colors forming the fluorescent film 3118. A metal back 3119 is formed from made of Al (aluminum) or the like on the surface of the fluorescent film 3118 on the rear plate 3115 side.
Terminals Dx1 to DxM, Dy1 to DyN, and Hv are connection terminals for the airtight structure provided to electrically connect the display panel to a driving circuit (to be described later). The terminals Dx1 to DxM are electrically connected to the row wirings 3113 of the multi electron source; Dy1 to DyN, to the column wirings 3114 of the multi electron source; and Hv, to the metal back 3119.
The interior of the airtight container is kept at a vacuum of about 10xe2x88x926 Torr. As the display area of the image display apparatus increases, demand is arising for any means for preventing deformation or destruction of the rear and face plates 3115 and 3117 caused by the difference between inner and outer pressures of the airtight container. If destruction is prevented by making the rear and facing plates 3115 and 3117 thick, this increases the weight of the image display apparatus, and generates distortion and parallax of an image when viewed diagonally. For this reason, the display panel in FIG. 31 adopts a structure support (to be referred to as a spacer or rib) 3120 which is made of a relatively thin glass plate and supports the airtight container against the atmospheric pressure. This spacer generally keeps the interval between the substrate 3111 having the multi electron source and the face plate 3117 having the fluorescent film 3118 at sub-mm to several mm, thereby keeping the interior of the airtight container in a high-vacuum state, as described above.
When a voltage is applied to respective cold cathode devices 3112 via the external terminals Dx1 to DxM and Dy1, to DyN, the image display apparatus using the above display panel emits electrons from the cold cathode devices 3112. At the same time, a high voltage of several hundred V to several kV is applied to the metal back 3119 via the external terminal Hv to accelerate the emitted electrons and collide them against the face plate 3117. Then, fluorescent substances of respective colors in the fluorescent film 3118 are excited to emit light, thereby displaying a color image.
One side (upper surface) of the structure support (spacer) 3120 is joined to the metal back 3119 for applying a high voltage, and the lower surface is mounted on the row wiring. In driving the display panel, the upper surface of the spacer 3120 receives a high voltage, and its lower surface receives a scanning voltage.
In FIG. 31, a conductive film material (e.g., NiO) or the like is deposited on the entire surface of the spacer 3120. This conductive film is formed to make the electric field inside the display panel uniform upon application of a high voltage. The film resistance is set to a resistance value of about 1xc3x97108 to 1xc3x97109.
Accordingly, a current (to be referred to as a spacer current) from the high-voltage source flows from the metal back 3119 to the row wiring via the spacer 3120.
FIG. 32 is a sectional view showing a display panel for an image display apparatus using a multi electron source manufactured by the present inventors.
For the illustrative convenience, FIG. 32 does not show any row and column wirings and the like on the substrate 3111 and shows only one cold cathode device 3112 (surface-conduction emission type device in FIG. 32) in a matrix layout. The metal back 3119 having an anode electrode, fluorescent substance, and the like is formed at a position where the metal back 3119 faces the substrate 3111. The substrate 311, face plate, and support frame (not shown) form a vacuum container. The cold cathode device 3112 is incorporated in the high-vacuum container. Reference numeral 4104 denotes a signal source for driving the cold cathode device 3112; and 4105, a high-voltage source for applying a high voltage between the substrate 3111 and metal back 3119. As shown in FIG. 32, electrons emitted by the cold cathode device 3112 are attracted upward by the metal back 3119 receiving a high voltage from the high-voltage source 4105, and collide against the fluorescent substance facing the cold cathode device 3112.
In some cases, unexpected discharge occurs in the container in which electron-emitting devices are arranged. The unexpected discharge may damage electron-emitting devices and wirings such as row and column wirings to a non-negligible degree. If unexpected discharge frequently occurs, problems arise.
When the above image display apparatus is used in a very severe environment or used abnormally, faults abruptly occur in the image display apparatus. For example, static electricity influences the driving circuit in a very dry environment, or heat, which is difficult to dissipate at a very high ambient temperature, influences operation of the driving circuit system.
One aspect according to the present invention has the following arrangement.
An image display apparatus comprises a display panel, and detection means for detecting a state of the display panel, wherein the image display apparatus is controlled in accordance with the state of the display panel.
Since the arrangement of this aspect adopts the detection means, the state of the display panel can be detected to control the image display apparatus at good timing. In particular, the present invention can preferably prolong the service life of the display panel under this control and suppress deterioration of characteristics to allow using the display panel for a long time. From this viewpoint, a desirable detection device is performed in a non-destructive condition in order to detect the state of the display panel.
The state of the display panel is preferably electrically detected.
For example, the state of the display panel can be detected by detecting a current flowing through the display panel, and especially a current flowing through an electrode arranged on the display panel.
When the display panel comprises an electron source and an acceleration electrode for accelerating an electron output from the electron source, the detection means detects a current flowing through the acceleration electrode.
The state of the display panel is preferably detected at a plurality of portions on the display panel, e.g., by measuring currents flowing through a plurality of portions on the display panel. Detection at the plurality of portions enables detecting the state of the display panel in units of the plurality of portions.
For example, when the display panel comprises an electron source and a plurality of acceleration electrodes for accelerating electrons output from the electron source, the detection means individually detects currents flowing through the plurality of acceleration electrodes.
The display panel may comprise an electron source and an acceleration electrode for accelerating an electron output from the electron source, and the detection means may detect a current flowing through a current path between the electron source and the acceleration electrode. The current path is set by a structure arranged between the electron source and the acceleration electrode. For example, the structure is a spacer for maintaining the interval between the electron source and the front plate on which the acceleration electrode, fluorescent substance, or the like is arranged. If a current flowing through the current path is not directly detected, this current can be indirectly detected by detecting a current flowing through the acceleration electrode or the potential of the acceleration electrode. This current path is preferably arranged outside the image formation area within the display panel.
The display panel may comprise an electron source, and the electron source may comprise an electron-emitting device for emitting an electron for displaying an image, and an electron-emitting device arranged to detect the state of the display panel. In this case, the electron-emitting device arranged to detect the state of the display panel is preferably set outside the image display area.
The display panel may comprise an electron source, an acceleration electrode for accelerating an electron output from the electron source, and an electron capture electrode arranged to detect the state of the display panel. In particular, a potential applied to the electron capture electrode is preferably closer to the potential of the electron source than the potential of the acceleration electrode for accelerating an electron for displaying an image. An electron-emitting device for outputting an electron to the electron capture electrode may be arranged separately from the electron-emitting device for emitting an electron for forming an image.
The detection means may detect the state of the display panel by detecting a potential of the display panel.
The detection means detects the state of the display panel by detecting a potential of an electrode arranged in the display panel.
The display panel may comprise an electron-emitting device, and the detection means may detect the state of the display panel by detecting a potential of an electrode electrically isolated from the electron-emitting device.
The display panel may comprise an electron source for outputting electrons, and the detection means may detect the state of the display panel by detecting a potential of an electrode arranged on the electron source.
When the display panel may comprise an electron source for outputting electrons, the state of the display panel may be detected while no electron is emitted by the electron source. Consequently, the state of the display panel can be detected while reducing the influence of output of electrons from the electron source. For example, when the display panel comprises an electron source having a plurality of electron-emitting devices and the electron source outputs electrons from respective electron-emitting devices while sequentially switching electron-emitting devices selected from the plurality of electron-emitting devices, the state of the display panel is detected when electron-emitting devices to be selected are switched.
The detection means detects discharge in the display panel, or even if discharge is not directly detected, detects a state about discharge. The detection means may detect a state about power consumption in the display panel such that the detection means detects a current flowing through the spacer.
The detection means may detect a change in state of the display panel.
If the image display apparatus comprises memory means for storing information detected by the detection means, the state of the panel can be preferably recorded.
The memory means stores information about the number of abnormalities in the display panel, information about a generation location of an abnormality in the display panel, or information about either one or both of a generation time and/or date and an end time and/or date of an abnormality in the display panel.
Control of the image display apparatus in accordance with the state of the display panel is transfer of information by information transfer means. As the information transfer means, means using visual display or means for generating voice can be preferably used.
Control of the image display apparatus in accordance with the state of the display panel is control of transferring information for prompting an information receiving person to control the image display apparatus. The information receiving person, e.g., the user of the image display apparatus or the maintenance personnel of the image display apparatus can control to suppress the progress of the abnormality in accordance with the transferred information.
Control of the image display apparatus in accordance with the state of the display panel may be control of a driving voltage of the display panel. If the state of the display panel becomes abnormal, the progress of the abnormality can be suppressed by decreasing the driving voltage of the display panel. More specifically, when the display panel comprises an electron source and an acceleration electrode for accelerating an electron output from the electron source, the voltage to be controlled is a voltage between the electron source and the acceleration electrode. When the display panel comprises an electron source for emitting an electron upon application of a voltage, the voltage to be controlled is the voltage for emitting an electron.
When the display panel comprises an airtight container for keeping an internal pressure lower than an ambient pressure, control of the image display apparatus in accordance with the state of the display panel may be control of increasing a vacuum degree in the airtight container. For example, the vacuum degree can be increased by containing a getter set in the airtight container in an atmosphere substance by heating or the like.
Control of the image display apparatus in accordance with the state of the display panel is selected preferably from a plurality of control operations, and more preferably from a plurality of control operations in accordance with the state of the display panel.
The display panel may comprise an electron source, and the electron source may have a plurality of electron-emitting devices connected in a matrix by a plurality of first wirings and a plurality of second wirings extending in a direction intersecting to the first wirings.
The display panel may comprise an electron source, and the electron source may comprise a cold cathode device.
The above aspects are particularly effective when the display panel is kept at a vacuum degree higher than an internal pressure of 10xe2x88x924 Torr when no abnormality occurs.
The present invention includes a television and computer display to which the above aspects are applied.
A method of controlling an image display apparatus according to the present invention has the following steps.
A method of controlling an image display apparatus having a display panel comprises steps of detecting a state of the display panel, and controlling the image display apparatus in accordance with the detected state.
The electron source can be one having a ladder-like layout in which a plurality of rows (to be referred to as a row direction hereinafter) of a plurality of cold cathode devices arranged parallel and each having two electrodes connected are arranged, and electrons emitted by the cold cathode devices are controlled by a control electrode (to be referred to as a grid hereinafter) arranged above the cold cathode devices along the direction (to be referred to as a column direction hereinafter) intersecting to this wiring.
According to the concepts of the present invention, the image display apparatus is not limited to an image forming apparatus suitable for display, and can also be used as a light-emitting source instead of a light-emitting diode for an optical printer made up of a photosensitive drum, light-emitting diode, and the like. At this time, by properly selecting M row wirings and N column wirings, the image display apparatus can be applied as not only a linear light-emitting source but also a two-dimensional light-emitting source. In this case, the image forming member is not limited to a substance which directly emits light, such as a fluorescent substance used in the following embodiments, but may be a member on which a latent image is formed by charging of electrons.
According to the concept of the present invention, the present invention can be applied to an electron-beam apparatus such as an electron microscope in which the target member to be irradiated with electrons emitted by the electron source is not an image forming member such as a fluorescent substance. Hence, the present invention can be adopted as a general electron-beam apparatus which does not specify any target member to be irradiated.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.